Method of construction of a boat hull

ABSTRACT

This invention relates to a method of boat hull construction. The method comprises mounting a former having an external configuration conforming to the internal configuration of the hull to a vacuum forming bed, heating a sheet of thermo-plastic material, supporting the heated sheet above the former by supporting one side of the sheet material on a first frame member, and supporting the opposed sides of the sheet to each side of the one side from a pair of second frame members. The second frame members are pivotally mounted to the first frame member about an axis perpendicular to the plane of the sheet material. On lowering the sheet over the former air is extracted from the space between the former and sheet material.

This invention relates to boat construction and in particular theconstruction of a boat hull utilising thermo-plastic materials.

In the past, formation of boat hulls using thermo-plastic material byvacuum forming methods have been unsuccessful as a result of significantunequal stretching of the material which results in a significantreduction in the thickness of the hull at particular zones in the hull.

It is an object of this invention to provide a method of hullconstruction which reduces the unequal stretching of the thermo-plasticmaterial during vacuum forming.

In one form the invention resides in a method of boat hull constructioncomprising mounting a former having an external configuration conformingto the internal configuration of the hull to a vacuum forming bed,heating a sheet of thermo-plastic material, supporting the heated sheetabove the former by supporting one side of the sheet material on a firstframe member, and supporting the opposed sides of the sheet to each sideof the one side from a pair of second frame members which are pivotallymounted to the first frame member about an axis perpendicular to theplane of the sheet material, and lowering the sheet over the former andextracting air from the space between the former and sheet material.

According to a preferred feature of the invention the second frames areresiliently restrained from movement towards each other.

According to a preferred feature of the invention the rear portion ofthe former engaged by the unsupported side of the sheet forms thetransom of the boat and has a transverse concave profile.

According to a preferred feature of the invention of the previousfeature the former is provided with a panel member having an edge ofcomplementary profile to the face of the rear portion of the formerwherein said panel is moved to overlie the formed sheet material beyondsaid portion to clamp it to the bed wherein said edge is closelyadjacent said rear portion.

In another form the invention results in a vacuum forming apparatushaving a vacuum forming bed, a former supported on said bed, said formerhaving the external configuration conforming to the internalconfiguration of a boat hull, a thermo-plastic sheet support comprisinga first frame member and a pair of second frame members pivotallysupported from the first frame member to define a substantially squareor rectangular planar space having an open side whereby said secondframe members are pivotally movable towards each other said first andsecond frame members are adapted to clampingly support a sheet ofthermo-plastic material.

According to a preferred feature of the invention the second framemembers are resiliently restrained from pivotable movement towards eachother.

According to a preferred feature of the invention the rear portion ofthe former engaged by the unsupported side of the sheet forms thetransom of the boat hull and has a transverse concave profile.

According to a preferred feature of the previous feature the apparatusfurther comprises a panel member having an edge profile complementary tothe profile of the rear portion of the former, said panel being movableto a position overlying the vacuum forming bed with its edge closelyadjacent the rear portion of the former.

The invention will be more fully understood in the light of thefollowing description of one specific embodiment. The description ismade with reference to the accompanying drawings of which:

FIG. 1 is a schematic sectional elevation of a forming installationaccording to the embodiments;

FIG. 2 is a schematic isometric view of the former and support frameaccording to the embodiment prior to application of the sheet materialover the former;

FIG. 3 is a schematic isometric view of the former and frame membersubsequent to the application of the sheet material over the former;

FIG. 4 is an isometric view of a boat hull according to the embodiment;

FIG. 5 is an inverted plant view of a boat hull according to theembodiment;

FIG. 6 is a plan view of a boat hull according to the embodiment;

FIG. 7 is a front elevation of a boat hull according to the embodiment;

FIG. 8 is a rear elevation of a boat hull according to the embodiment;and

FIG. 9 is a side elevation of a boat hull according to the embodiment.

The embodiment relates to a method of construction of a boat hullutilising thermo-plastic sheet material by a vacuum forming process. Toform the boat hull a former 51 having the desired configuration of theboat hull is produced whereby the transom 13 has a substantiallytransverse concave configuration. The former 51 is applied to a vacuumbed 52 which is of a substantially conventional form to that used in thevacuum forming of thermo-plastic sheet material. The rear edge of theformer 53 adjacent the rear portion of the former which forms thetransom 13 of the boat hull supports a panel 60 which is pivotable abouta transverse axis. The free edge of the panel has an edge 61complementary to the profile of the rear portion such that when thepanel is pivoted to overlie the vacuum bed 52 the edge lies closelyadjacent to the rear portion of the former.

The vacuum table 53 is associated with a substantially rectangular frame56 which is supported above the vacuum table by a plurality of supports57 such as jacks which enable the frame to be lowered onto the vacuumtable 53 or raised therefrom. The frame 56 has a first frame member 58which pivotally supports a pair of second substantially parallel framemembers 59 which extend the length of the vacuum bed 52. Each secondframe member 59 is pivotally mounted to the first frame member about atransverse axis thereof. The second frame members are connected to thesupport frame 16 by a set of springs 54 to control the movement of thesecond frame members 59 towards each other. The first and second framemembers 58 and 59 are adapted to clampingly engage a sheet ofthermo-plastic sheet material 55. In use the frame member 56 is raisedfrom the vacuum table 53 and a sheet of thermo-plastic sheet material isfixed to the first and second frame members such that one end is clampedto the one end 58 of the frame member 56 and the sides are clamped tothe respective second frame members 59. The sheet material is thenheated by known means which may comprise a convection oven or infraredradiation and when heated sufficiently it is lowered over the formerwhereby due to the plasticity created as a result of the heating of thesheet 55 it will drape over the former 51 to substantially conform tothe shape thereover. Air is then extracted from the space between theformer and the sheet material 55 by utilisation of the air extractionmeans on the vacuum table 52 which causes the sheet material to closelyconform to the configuration of the former. To form the transom thepanel 60 is pivoted to overlie the sheet material overlying the vacuumbed 52 to the rear of the rear portion of the former and between thesecond frame members to shape the sheet to the desired configuration ofthe transom as formed by the rear portion of the former prior to theapplication of the vacuum.

On lowering the frame 56 over the former 51 the portion of the sheet 55supported by the one end of the frame 58, and the adjacent portions ofthe side frames 59 is stretched upon it engaging the portion of theformer which corresponds to the intended bow of the boat. Theconfiguration of this portion of the former is substantially continuousand therefore the degree of stretching applied to this sheet material isalso substantially continuous. The unsupported side of the sheetmaterial 55 will drape over the transom portion of the former and as aresult of that draping motion the side second frame members 59 will moveinwardly against the biasing force provided by the spring members 54 toensure that there is substantially minimal unequal stretching of thesheet material as it bends to conform to the edges provided by thejunction between the transom 52 and the sides and bottom of the hull andthe application of the panel 60 over the vacuum bed to the rear of theformer. Upon the sheet material having draped in to substantialconformity with the former the extraction of air between the former andthe sheet material serves to finalise such conformity. By allowing thesides of the sheet material in the region of the unsupported end to moveinwardly during the draping process ensures that there is a minimum ofstretching of the sheet material to the zones of discontinuity in theshape thereof to avoid a significant reduction in thickness of themoulded hull at such zones.

As shown in the drawings the boat hull 11 produced by the embodiment hasa bow of substantially conventional configuration while the transom 13is curved inwardly about at least two substantially upright axes toeither side of the transom whereby two rearward extensions 14 areprovided at each side of the hull.

A central portion 16 comprising a longitudinal raised panel extending toeach side of the central axis which extends for substantially the fulllength of the hull and is symmetrical about the longitudinal axis isprovided along the bottom of the hull. The central portion of thetransom 13 is formed with an inwardly stepped portion 15 which is ofconvergent depth between the upper edge of the transom and of thecentral portion 16. The presence of the stepped portion 15 in thetransom is provided to compensate for the presence of the centralportion 16 in the bottom of the hull during the vacuum forming processto minimise the degree of stretching of the thermo-plastic sheetmaterial in the junction of the fledged portion with the transom 13.

Each side 17 of the hull is formed with an outwardly extending rib 18which extends substantially the full length of the hull and is formed bya channel member provided on the former and which is removable from theformer on removal of the formed hull therefrom. On removal of the hullfrom the former, the channel member is then removed from the formed hullto provide a channel-shaped recess on the internal face of the side wall18. The channel-shaped recess provided by the internal face of the rib18 is used to accommodate a thwart 19 which is located by beingresiliently deformed on introduction into the channel between the side17 of the boat hull and is subsequently riveted into place.

The presence of the rearward extensions 14 to each side of the hull 11as a result of the inwardly curved transom 13 serve to increase thebuoyancy of the hull at the rear portion thereof. The presence of suchbuoyancy serves to counteract the tendency of the transom 13 to sinklower in the water on the presence of a load thereat as a result of thepresence of an outboard motor and/or occupant at the rear of the boat.In addition, the presence of a curved transom serves to move the weightof the outboard motor forwardly in relation to the overall length of theboat and serves to protect the outboard motor from physical damage whenthe hull is moored at jetties and is adjacent to other boats.

The presence of the central portion 16 in the bottom of the boat hullserves to enhance the lateral stability of the hull when moving throughthe water and ensures substantially direct tracking of the boat hull inits movement to reduce the degree of sidewards "slip" of the boat hullwhen changing direction.

It should be appreciated that the scope of the present invention neednot be limited to the particular scope of the embodiment describedabove.

It will be appreciated that the hull may take any suitableconfiguration. If desired the ribs 18 may be replaced by an inwardlydirected step spaced downwardly from the gunwale which can support thethwarts. In addition the thwarts can be associated with buoyancy cellsfixed between the underneath of the thwart and the boat hull. Inaddition the central portion 16 and the thwart 19 can be replaced by acentral longitudinal rib or keel and a set of longitudinal ribs to eachside thereof.

The claims defining the invention are as follows:
 1. A method ofconstructing a boat hull from a planar sheet of thermoplastic material,said sheet having an end portion extending between two opposed sideportions, said boat hull having a desired internal configuration, saidmethod comprising:a) mounting a former having an external configurationconforming to said internal hull configuration to a vacuum-forming bed;b) heating said sheet of thermoplastic material; c) supporting saidheated sheet above said former on a frame by supporting said end portionon a first frame member and by supporting said opposed sides of saidsheet from a pair of second frame members articulated to said firstframe member in a manner permitting relative movement between saidsecond frame members about an axis transverse to the plane of said sheetfor the control of said sheet during forming; d) lowering said frame andsheet over said former thereby defining a space with said former; and e)extracting air from said space between said former and saidthermoplastic material sheet to conform said sheet to said former.
 2. Amethod of constructing a boat hull as claimed in claim 1 wherein saidsecond frame members are resiliently restrained from movement towardseach other.
 3. A method of constructing a boat hull according to claim 1wherein said second frame members are elongated to extend away from saidfirst frame member and are pivotally mounted to said first frame memberto be swingable towards and away from one another about said axistransverse to the plane of said sheet material.
 4. A method ofconstructing a boat hull according to claim 1 wherein said sheet has anunsupported sheet portion extending between said second frame membersremotely from said first frame member and said former has a rear portionwith a transverse concave profile and wherein said rear portion of saidformer is engaged by said unsupported sheet portion to form a transomfor said boat hull.
 5. A method of constructing a boat hull as claimedin claim 4 wherein said lowered sheet extends rearwardly beyond saidrear former portion and said former includes a panel member having anedge of complementary shape to a transverse profile of said rear portionof said former wherein said panel is moved to overlie said sheetmaterial on said former beyond said portion to clamp it to saidvacuum-forming bed and wherein said edge engages said sheet to hold saidsheet closely conforming to said rear portion transverse profile.
 6. Amethod of constructing a boat hull according to claim 1 wherein saidsecond frame members are elongated to extend away from said first framemember, are pivotally mounted to said first frame member to be swingabletowards and away from one another about said axis transverse to theplane of said sheet material and are resiliently restrained frommovement towards each other.
 7. A method of constructing a boat hullaccording to claim 6 wherein said sheet has an unsupported sheet portionextending between said second frame members remotely from said firstframe member and said former has a rear portion with a transverseconcave profile and wherein said rear portion of said former is engagedby said unsupported sheet portion to form a transom for said boat hull.8. A boat hull constructed by the method of claim
 1. 9. A vacuum-formingapparatus for constructing a boat hull by molding a thermoplasticmaterial sheet on a former, said boat hull having a desired internalconfiguration, said vacuum-forming apparatus comprising:a) a vacuumforming bed; b) a former supported on said bed, said former having anexternal configuration conforming to said boat hull internalconfiguration; c) an open-ended frame to support and tension saidthermoplastic material sheet, said frame being configured with arms toembrace said former and being lowerable around said former to apply saidthermoplastic material sheet over said former, said arms havingextremities defining an open end to said frame, said frame arms beingrelatively movable towards and away from each other; d) resilient meansfor controlling relative movement of said frame arms; and e) means toattach said sheet to said frame to be supported by said frame with anunsupported side at said open frame end;whereby said sheet can belowered over said former with tension in said sheet being controlled byresiliently controlled movement of said frame arms.
 10. An apparatus asclaimed in claim 9 wherein said former has a rear portion shaped with atransverse concave profile to be engaged by said unsupported side ofsaid sheet to form a transom of the boat hull.
 11. An apparatus asclaimed in claim 9 further comprising a panel member having an edgeshaped to be complementary to said transverse profile of said rearformer portion said panel being movable to a position overlying saidvacuum-forming bed with said panel member edge closely conforming tosaid rear former portion transverse profile.
 12. An apparatus as claimedin claim 9 wherein said frame comprises a first frame member and saidframe arms are constituted by a pair of second frame members pivotallysecured to said first frame member to define a substantially rectangularplanar space having an open side.
 13. An apparatus as claimed in claim 9wherein said frame includes side members extending alongside andoutwardly of said arms, said resilient controlling means acting betweenrespective ones of said side members and said arms.
 14. An apparatus asclaimed in claim 13 wherein said frame includes side members extendingalongside and outwardly of said arms, said resilient controlling meansacting between respective ones of said side members and said arms. 15.An apparatus as claimed in claim 14 wherein said former has a rearportion shaped with a transverse concave profile to be engaged by saidunsupported side of said sheet to form a transom of the boat hull. 16.An apparatus as claimed in claim 15 further comprising a panel memberhaving an edge shaped to be complementary to said transverse profile ofsaid rear former portion, said panel being movable to a positionoverlying said vacuum-forming bed with said panel member edge closelyconforming to said rear former portion transverse profile.